1. Field of the Invention
The present invention relates to a coating composition that improves the adhesion of toners to receiving substrates, such as paper. More particularly, the invention relates to a toner recording medium including a particular coating composition and a process for producing that toner recording medium.
2. Description of the Prior Art
The use of electrographic means to produce a variety of images for different applications is continuing to expand. Examples of the imaging technologies being employed include electrophotography, magnetography, electrostatics, ink jet, thermal transfer, etc. The materials used to generate the visible images can be dry or liquid toners or aqueous-based, solvent-based or hot melt-based inks. The imaging materials may be fused to the substrate by heat, pressure, a combination thereof or by solvation in the case of toners. There is a need for improved adhesion of toners to substrates to prevent smudging, smearing and flaking of the image encountered in subsequent handling.
In general, paper is used as the imaging substrate in these systems. It has been found that the degree of fuse quality varies with the grade and source of paper used. Also, it is sometimes desirable to image on substrates other than paper such as labels, plastic films, metal foils or textiles.
Prior art uses of coated paper have primarily been directed to ink jet recording uses. Polymeric binders and pigments or particulate silica have been used to form coated substrates for ink jet recording paper and optical bar code printing. Generally, the coatings applied have been in a coating weight of greater than 2 g/m.sup.2 per side of the substrate.
U.S. Pat. No. 4,440,827 to Miyamoto et al. discloses a process for producing a recording paper for ink jet recording and optical bar code printing, the recording paper including a coating layer of an inorganic pigment and an aqueous polymeric binder. The coating is applied by two or more coating steps and the patent discloses that it is necessary for the total amount of coating per one side to be 10 g/m.sup.2 or more, preferably 10 to 25 g/m.sup.2.
U.S. Pat. No. 4,478,910 to Oshima et al. discloses ink jet recording paper including a base sheet with a coating layer comprising particulate fine silica particles in a water soluble polymeric binder. The coating layer comprises fine silica particles having a specific surface area of more than 200 m.sup.2 /g and a water soluble polymeric binder. The preferred coating amount on one side of the substrate is disclosed as between 3-12 g/m.sup.2 and the actual coating weights exemplified range from 6-12 g/m.sup.2.
U.S. Pat. No. 4,269,891 to Minagawa discloses an ink jet recording sheet having a support and an ink absorbing layer thereon. The ink absorbing layer comprises a white pigment and a binder resin, with the weight ratio of pigment to binder ranging from 0.2 to 10. It is disclosed that the ink absorbing power of the ink absorbing layer must be about 1.5 to 18.0 mm/min. Minagawa discloses that a thickness of the coating layer must be at least about 3 micrometers to attain the favorable ink absorbing power.
U.S. Pat. No. 4,758,461 to Akiya et al. discloses an ink jet recording paper comprising a substrate including a silicon-containing type pigment and a fibrous material present in a mixed state. The recording paper has a Stockigt sizing degree that can not exceed 15 sec. and a coating weight that can not be less than 2 g/m.sup.2.
U.S. Pat. No. 4,425,405 to Murakami et al. discloses an ink jet recording sheet comprising a paper support containing a composition of an aqueous dispersion of a binder resin and a white filler. The binder resin is polyvinylpyrrolidone, vinylpyrrolidone-vinylacetate copolymer, or a mixture thereof. The composition is applied in an amount of 3 to 50 g/m.sup.2 on a dry basis.
U.S. Pat. No. 4,474,847 to Schroder et al. discloses ink jet recording paper that includes a coating of a pigment and/or filler of non-flake structure and a binding agent. The pigment is disclosed as being at least 90% by weight of the dried coating.
Each of the foregoing patents relates to a coated paper for use as ink jet recording paper. There exists a need for a paper that can function as a recording medium for toner imaging that will provide improved adhesion of toners and will resist smudging, smearing and flaking of the toner image in subsequent handling.
The present inventors have found that a toner recording medium obtained by coating a substrate with a dispersion of particulate silica and a polyvinyl alcohol binder to a coating weight of less than 2 g/m.sup.2 per side of the substrate provides improved adhesion and reduced smudging, smearing and flaking when using a number of varied substrates including paper, plastic films, metal foils and textiles.